.TH biosnoop 8  "2015-09-16" "USER COMMANDS"
.SH NAME
biosnoop \- Trace block device I/O and print details incl. issuing PID.
.SH SYNOPSIS
.B biosnoop [\-h] [\-Q] [\-d DISK] [\-P]
.SH DESCRIPTION
This tools traces block device I/O (disk I/O), and prints a one-line summary
for each I/O showing various details. These include the latency from the time of
issue to the device to its completion, and the PID and process name from when
the I/O was first created (which usually identifies the responsible process).

This uses in-kernel eBPF maps to cache process details (PID and comm) by I/O
request, as well as a starting timestamp for calculating I/O latency.

This works by tracing various kernel blk_*() functions using dynamic tracing,
and will need updating to match any changes to these functions.

This makes use of a Linux 4.4 feature (bpf_perf_event_output());
for kernels older than 4.4, see the version under tools/old,
which uses an older mechanism

Since this uses BPF, only the root user can use this tool.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH OPTIONS
.TP
\-h
Print usage message.
.TP
\-Q
Include a column showing the time spent queued in the OS.
.TP
\-d DISK
Trace this disk only.
.TP
\-P
Display block I/O pattern (sequential or random).
.SH EXAMPLES
.TP
Trace all block device I/O and print a summary line per I/O:
#
.B biosnoop
.SH FIELDS
.TP
TIME(s)
Time of the I/O completion, in seconds since the first I/O was seen.
.TP
COMM
Cached process name, if present. This usually (but isn't guaranteed) to identify
the responsible process for the I/O.
.TP
PID
Cached process ID, if present. This usually (but isn't guaranteed) to identify
the responsible process for the I/O.
.TP
DISK
Disk device name.
.TP
T
Type of I/O: R = read, W = write. This is a simplification.
.TP
SECTOR
Device sector for the I/O.
.TP
BYTES
Size of the I/O, in bytes.
.TP
QUE(ms)
Time the I/O was queued in the OS before being issued to the device,
in milliseconds.
.TP
LAT(ms)
Time for the I/O (latency) from the issue to the device, to its completion,
in milliseconds.
.SH OVERHEAD
Since block device I/O usually has a relatively low frequency (< 10,000/s),
the overhead for this tool is expected to be negligible. For high IOPS storage
systems, test and quantify before use.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Brendan Gregg, Rocky Xing
.SH SEE ALSO
disksnoop(8), iostat(1)
